全文获取类型
收费全文 | 121266篇 |
免费 | 10604篇 |
国内免费 | 17910篇 |
专业分类
化学 | 81143篇 |
晶体学 | 1908篇 |
力学 | 7097篇 |
综合类 | 1608篇 |
数学 | 27036篇 |
物理学 | 30988篇 |
出版年
2024年 | 147篇 |
2023年 | 1178篇 |
2022年 | 2164篇 |
2021年 | 2589篇 |
2020年 | 3109篇 |
2019年 | 3228篇 |
2018年 | 2840篇 |
2017年 | 3443篇 |
2016年 | 3969篇 |
2015年 | 3681篇 |
2014年 | 5063篇 |
2013年 | 9207篇 |
2012年 | 5976篇 |
2011年 | 6896篇 |
2010年 | 5836篇 |
2009年 | 7408篇 |
2008年 | 7934篇 |
2007年 | 8199篇 |
2006年 | 7762篇 |
2005年 | 6938篇 |
2004年 | 6429篇 |
2003年 | 5820篇 |
2002年 | 4935篇 |
2001年 | 4025篇 |
2000年 | 3843篇 |
1999年 | 3445篇 |
1998年 | 3133篇 |
1997年 | 2644篇 |
1996年 | 2262篇 |
1995年 | 2134篇 |
1994年 | 1950篇 |
1993年 | 1684篇 |
1992年 | 1556篇 |
1991年 | 1138篇 |
1990年 | 895篇 |
1989年 | 788篇 |
1988年 | 708篇 |
1987年 | 524篇 |
1986年 | 453篇 |
1985年 | 515篇 |
1984年 | 493篇 |
1983年 | 241篇 |
1982年 | 379篇 |
1981年 | 442篇 |
1980年 | 348篇 |
1979年 | 324篇 |
1978年 | 247篇 |
1977年 | 225篇 |
1976年 | 170篇 |
1974年 | 116篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Yuanbo Gao Tingting Yang Xueli Wang Jizong Chen Yong He 《Journal of polymer science. Part A, Polymer chemistry》2022,60(10):1610-1623
Two series of novel alternating copolyoxamides (PAnT-alt-n2 and PAn2-alt-62) are synthesized via solution/solid-state polycondensation (SSP). The alternating structures are analyzed carefully with 1H NMR and 13C NMR spectra. The melting behaviors, thermal stabilities, crystal structures and crystallinities are systematically evaluated by DSC, TGA and WAXD. The results reveal that these alternating copolyoxamides possess almost perfect alternating chain structures and have high melting temperature (Tm > 270 °C), high crystallinity (Xc > 32%) and high decomposition temperature (T5 > 405 °C) as well as low saturated water absorption (<3.5 wt%), which suggests that they have high potential as engineering plastic of high heat resistant. 相似文献
2.
Patrick Imrie Jianyong Jin 《Journal of polymer science. Part A, Polymer chemistry》2022,60(2):149-174
4D printing is an exciting branch of additive manufacturing. It relies on established 3D printing techniques to fabricate objects in much the same way. However, structures which fall into the 4D printed category have the ability to change with time, hence the “extra dimension.” The common perception of 4D printed objects is that of macroscopic single-material structures limited to point-to-point shape change only, in response to either heat or water. However, in the area of polymer 4D printing, recent advancements challenge this understanding. A host of new polymeric materials have been designed which display a variety of wonderful effects brought about by unconventional stimuli, and advanced additive manufacturing techniques have been developed to accommodate them. As a result, the horizons of polymer 4D printing have been broadened beyond what was initially thought possible. In this review, we showcase the many studies which evolve the very definition of polymer 4D printing, and reveal emerging areas of research integral to its advancement. 相似文献
3.
4.
Qianqian Fan Zirui Liu Feng Qiu Prof. Yong Mao Prof. Qingju Liu Prof. Longzhou Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(63):e202202700
The artificially accurate design of nonmetal electrocatalysts’ active site has been a huge challenge because no pure active species with the specific structure could be strictly controlled by traditional synthetic methods. Species with a multiconfiguration in the catalyst hinder identification of the active site and the subsequent comprehension of the reaction mechanism. We have developed a novel electro-assisted molecular assembly strategy to obtain a pure pentagon ring on perfect graphene avoiding other reconstructed structures. More importantly, the active atom was confirmed by the subtle passivation process as the topmost carbon atom. Recognition of the carbon-defect electrocatalysis reaction mechanism was first downsized to the single-atom scale from the experimental perspective. It is expected that this innovative electro-assisted molecular assembly strategy could be extensively applied in the active structure-controlled synthesis of nonmetal electrocatalysts and verification of the exact active atom. 相似文献
5.
6.
《Operations Research Letters》2022,50(2):137-144
In mine planning problems, cutoff grade optimization defines a threshold at every time period such that material above this value is processed, and the rest is considered waste. In orebodies with multiple minerals, which occur in practice, the natural extension is to consider a cutoff surface. We show that in two dimensions the optimal solution is a line, and in n dimensions it is a hyperplane. 相似文献
7.
8.
Kento Nishikibe Keisuke Nishikawa Momochika Kumagai Matsumi Doe Yoshiki Morimoto 《化学:亚洲杂志》2022,17(1):e202101137
There are marine cytotoxic bromotriterpenoids, named the thyrsiferol family that are structurally characterized by some tetrahydropyran (THP) and tetrahydrofuran (THF) rings. The thyrsiferol family belongs to natural products that are often difficult to determine their stereostructures even by the current, highly advanced spectroscopic methods, especially in acyclic systems including stereogenic tetrasubstituted carbon centers. In such cases, it is effective to predict and synthesize the possible stereostructures. Herein, to elucidate ambiguous stereostructures and unassigned absolute configurations of aplysiol B, laurenmariannol, and saiyacenol A, members of the thyrsiferol family, we carried out their asymmetric chemical syntheses featuring 6-exo and 5-exo oxacyclizations of epoxy alcohol precursors and 6-endo bromoetherification of a bishomoallylic alcohol. In this paper, we report total assignments of their stereostructures through their asymmetric chemical syntheses and also their preliminary cytotoxic activities against some tumor cells. These results could not have been achieved without depending on asymmetric total synthesis. 相似文献
9.
This paper infers from a generalized Picone identity the uniqueness of the stable positive solution for a class of semilinear equations of superlinear indefinite type, as well as the uniqueness and global attractivity of the coexistence state in two generalized diffusive prototypes of the symbiotic and competing species models of Lotka–Volterra. The optimality of these uniqueness theorems reveals the tremendous strength of the Picone identity. 相似文献
10.
《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2021,38(5):1337-1371
In this paper we consider minimizers of the functional where is a bounded open set and where are the first k eigenvalues on Ω of an operator in divergence form with Dirichlet boundary condition and with Hölder continuous coefficients. We prove that the optimal sets have finite perimeter and that their free boundary is composed of a regular part, which is locally the graph of a -regular function, and a singular part, which is empty if , discrete if and of Hausdorff dimension at most if , for some . 相似文献